It is well known that mixed metal oxide powders can be prepared by cohydrolysis of metal alcoholates. For this purpose, dilute solutions of metal alcoholates in an alcohol are generally prepared and these solutions are mixed with an alcoholic solution of water. The reaction is generally performed under an inert nitrogen atmosphere, at ambient temperature. At the end of the process the mixed metal oxide powder which has precipitated is collected (Better Ceramics Through Chemistry-Materials Research Society Symposia Proceedings-Vol. 32--1984--Elsevier Science Publishing Co., Inc.-Bruce Fegley et al: "Synthesis, characterization, and processing of monosized ceramic powders", pages 187 to 197; Patent U.S.-A-4,543,341). This known process has been designed for the production of metal oxide powders of very high chemical purity, intended for use in ceramic materials.